Apparatus for treating waste materials

ABSTRACT

The method of treating waste materials, such as sewage, involves introducing raw sewage into a body of aqueous medium, aerating said body of aqueous medium to maintain solids in suspension and to effect B.O.D. removal, withdrawing a sufficient volume of liquid containing a minor amount of solids for discharge as a surcharge free sewage disposal effluent to compensate for the volume of influent waste material in order to maintain a relatively constant volume for said body of aqueous medium, said withdrawn liquid being the filtrate which has passed through a movable filter subject to submerged surface cleaning so that the filter medium while submerged in said body of aqueous medium is being maintained substantially free of solids that normally would accumulate on the filter medium during the filtration of the solids suspension and prevent loss of filtration capacity by directing streams of fluid medium against the outer surface of the filter medium as it passes through the body of aqueous medium.

United States Patent 11 1 Davidson et a1.

[ Jan.30,1973

[54] APPARATUS FOR TREATHNG WASTE MATERIALS [73] Assignee: FMCCorporation [22] Filed: April 15,1971

[21] Appl. N0.: 134,335

[52] U.S.Cl. ..2l0/391,2l0/7,210/l9, 210/77, 210/81, 210/384, 210/402,210/408 [51] Int. Cl. ..B0ld 33/06 [58] Field of Search....2l0/77, 81,19, 217, 391, 392, 210/402, 404, 407, 408; 162/318, 325, 357,

552,030 l/l958 Canada ..2l0/402 Primary Examiner-Michael RogersAttorney-Dressler, Goldsmith, Clement & Gordon [57] ABSTRACT The methodof treating waste materials, such as sewage, involves introducing rawsewage into a body of aqueous medium, aerating said body of aqueousmedium to maintain solids in suspension and to effect B.O.D. removal,withdrawing a sufficient volume of liquid containing a minor amount ofsolids for discharge as a surcharge free sewage disposal effluent tocompensate for the volume of influent waste material in order tomaintain a relatively constant volume for said body of aqueous medium,said withdrawn liquid being the filtrate which has passed through amovable filter subject to submerged surface cleaning so that the filtermedium while submerged in said body of aqueous medium is beingmaintained substantially free of solids that normally would accumulateon the filter medium during the filtration of the solids suspension andprevent loss of filtration capacity by directing streams of fluid mediumagainst the outer surface of the filter medium as it passes through thebody of aqueous medium.

1 Claim, 4 Drawing Figures APPARATUS FOR TREATING WASTE MATERKALS Thisinvention relates to the treatment of waste materials. Moreparticularly, it relates to a process for aerobic treatment of sewage.Still more particularly, it relates to a method and apparatus forreducing the Biochemical Oxygen Demand of an aqueous medium containingsewage and for processing greater quantities of sewage per unit volumeof the aeration tank without need for conventional associate settlingunits.

Briefly, the method for preparing clarified liquid medium from a liquidmedium containing suspended solids comprises introducing said liquidmedium into a container therefor, passing liquid within said containerthrough a movable porous element which separates a first zone for theliquid medium containing suspended solids from a second zone forclarified liquid medium which has passed through said porous element,moving said porous element through a predetermined path about saidsecond zone and maintaining the submerged surface thereof which isexposed to said suspension substantially free of solids during thefiltering of the suspension by the impinging action of streams of fluidmedium directed against said submerged surface and withdrawing clarifiedliquid medium from said second zone.

An apparatus for clarifying a liquid suspension comprises a containerfor said suspension means for introducing said liquid suspension intosaid container, a movable porous element which separates the introducedliquid suspension from a zone for clarified liquid, means submerged insaid suspension for directin g fluid into contact with said movableporous element to dislodge solids which are brought into contact withsaid element by the liquid that passes therethrough, said means fordirecting fluid submerged in said suspension being positioned adjacentthe surface area of said porous element through which liquid passes intosaid zone for clarified liquid, said dislodging of solids being effectedby impingement contact and means for discharging clarified liquid fromsaid zone therefor.

In the treatment to effect separation of solids from liquid suspensions,the suspension is generally delivered to a quiescent tank for gravitysettling of the solids or if faster separation is desired, to a tankequipped with a filter means having pores of a size to pass the liquidbut to prevent passage of at least a major portion of the particulatesolid matter. One of the primary disadvantages of gravity settling isthe length of time required to produce an effluent having a solidscontent of less than about 30 parts per million (ppm). A primarydisadvantage of filter means is that as solids are deposited on thescreen, cloth, paper, etc., the solids block more and more of the poresand reduce the quantity of liquid which can pass therethrough untileventually the operation must be interrupted for replacement of a newfilter means, or until the removed filter means can be subjected to suchcleaning treatments as acid washing, water washing, etc., to removesolids from the pores and restore the porosity and original filteringcapability.

Now it has been discovered, that suspensions of solids can be processedfor production of a clarified liquor in markedly increased quantities byeffecting a continuous submerged surface cleaning action to maintain thesurface of the porous medium facing the suspension of solidssubstantially free of solids during the stage when liquid passestherethrough by directing streams of gas or liquid against the filtersurface through which liquid is passing.

In one embodiment of the invention, as applied to the treatment ofsewage for significant reductions in Biochemical Oxygen Demand (B.O.D.)in an aerobic process, clarification of quantities of liquid of the sameorder of magnitude as that of the influent sewage is effected directlyfrom the suspension in the aeration tank while continuing to aerate thesuspension and the high and reasonably constant rate of passage ofliquid through the porous medium into an isolated accumulation zone forclarified liquor is maintained by cleaning action to keep that portionof the surface of the porous medium which is submerged in the suspensionand through which liquid is passing, free of solids.

Control over the volume of liquid in the tank is provided indirectly byflow control means associated with the outlet pipe for effluent beingwithdrawn from the drum.

The filtration apparatus may take numerous forms depending upon themanner in which the filter medium will be given secondary cleaningaction to keep the pores from becoming blinded by minute particles whichbecome wedged in the pores and are not removed by the impinging actionof the jets of fluid.

The form of secondary cleaning action will depend upon the manner inwhich the solids will be disposed. The solids can be dislodgedpreferably by ultrasonic vibrations created by a transducer or highpressure wash water jets operating in a direction opposite the directionof flow while filtration takes place, etc. When secondary cleaning iscarried out within the tank, ultrasonic vibrations are created by atransducer positioned to effect cleaning shortly before the filter meansmoves into the submerged position where liquid passes therethrough.

One form of movable filter medium may be a continuous filter screenwhich is guided through the aeration tank by a perforate drum. Such ascreen may be made up of fabric or metallic screening. Effectiveness ofsuch screens as filter medium depends upon the size of the pores. Whenoperating with a relatively high solids concentration in the liquidunder aeration, a cloth with a nominal hole size of 20 microns, willgenerally produce a filtrate with 40 ppm to ppm of solids. A screen ofnominal 10 micron hole size will generally produce a filtrate of lessersolids concentration. 4

A treatment plant of this type is capable of operating in a variety ofsystems. The system can be used in a tank designed for concentrating ofsolids, in an aeration tank of an aerobic digestion system, in theaeration tank of an activated sludge system, etc.

One form of apparatus for clarifying liquid suspensions inaccordancewith this method may consist of a tank for a suspension ofsolids, a perforate drum mounted for at least partial submergence insaid suspension, a continuous screen which is guided through the tank incontact with said drum and is a movable filter medium, fluid dischargemeans for dislodging solids brought into contact with said screen by theliquid passing therethrough, submerged in said suspension adjacent thearea where the screen and drum cooperate for passage of liquid into theinterior of said drum which remove solids by impingement contact andmeans for discharging clarified liquid from the interior of said drum.

In operations where a rotatable drum equipped with a porous surfacecapable of acting as a filter medium is completely submerged in thesuspension, it is necessary to establish conditions for maintenance ofatmospheric air pressure in that portion of the drum where air collects.Means for relieving the pressure developed by air trapped above theliquid outlet pipe, allows the hydraulic head difference between theliquid levels inside and outside the drum to maintain a fully effectivestraining capacity over substantially the entire screening surface.

The invention will be further understood from the following descriptionof preferred embodiments of the invention taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a perspective view of an aeration tank and a tank forconcentration of solids to be wasted and fluid jet means submerged inthe liquor with streams directed against the submerged portion of themovable filter screen;

FIG. 2 is a vertical sectional view of a tank having air dispersers tokeep solids in suspension, showing an end view of a rotatable drumhaving a porous surface to act as filter medium and air jets submergedin the suspension directed against the submerged surface of the drum;

FIG. 3 is a vertical sectional view along the line 33 of FIG. 2 havingair dispersers to keep solids in suspension and showing as a substitutefor the air jets, gas dispersers of a length co-extensive with that ofthe drum filter; and

FIG. 4 is a vertical sectional view of a tank having air dispersers tokeep solids in suspension and a rotatable drum having a porous surfaceto act as filter medium and a pumping system to withdraw liquor from thetank and return it to the tank through nozzles directing the liquidstreams against the submerged surface of the drum. 1

In FIG. 1, the numeral indicates a tank of suitable material ofconstruction. A solids suspension is introduced into tank 10 through aninfluent channel 11 which permits flow into the tank over a weir 12.Tank 10 is divided into an aeration compartment 13 and a solidsaccumulation compartment 14 by a wall 15.

Aeration in tank 10 is effected by introducing air through headers 16and dispersers 17 which delivers air from a conventional source notshown. Air dispersers 17 are provided with suitable control means forair flow, such as orifices, so that air flow from header 16 to thedispersers is balanced.

Liquid of the suspension passes through a movable endless screen 18.Endless screen 18 is guided through the compartment 13 by a rotatabledrum 19 which has a perforate peripheral area. Rotatable drum" 19 ismounted in a submerged position in the aeration compartment such thatthe level of liquid suspension in compartment 13 is above the outletports 20 for clarified liquid in the hollow central shaft 21 of drum 19.Shaft 21 communicates with outlet pipe 22 through a suitable packinggland or rotating seal 23.

As the endless screen 18 enters the liquid suspension and is guided in asubmerged path therethrough, the surface thereof is contacted by airstreams flowing from jets 24, 25 and 26 adopted with suitable controlmeans such as orifices. Air from jet 24 contacts the screen 18 duringits movement downwardly. Air from jet 25 contacts the screen in the areawhere travel direction changes from downwardly to upwardly and air fromjet 26 contacts the screen as it moves upwardly, thus keeping thesurface free of solids during its entire travel through the suspension.

The jet nozzles are positioned so that the effective impingement zonesspan the entire width of the screen 18. Operation of such jets may beintermittent if it is desired to have the screen act as one alternativeway for removing some solids out of the tank as a means of preventingthe solids content of the suspension from exceeding desired limits.

Any solids which may have been carried out of compartment 13 by screen18 are dislodged as the screen is submerged in the liquid in compartment14, preferably by an ultrasonic transducer 27, i.e., by sonicvibrations.

Movable screen 18 is power driven by motor means which is not shown,operating through drive pulley 28. After the screen has been sonicallycleaned, the screen is directed by means of idler pulleys 29 and 30 tothe compartment 13 where it begins another cycle.

Solids accumulated in compartment discharged through conduit 31.

In the embodiment illustrated in FIG. 2, the numeral 32 indicates a tankinto which a solids suspension is introduced by suitable means.

Liquid of the suspension passes through the porous peripheral surface 33of a rotatable drum 34. Rotatable drum 34 is completely submerged in thesuspension. Drum 34 rotates about a central shaft 35 which has a centralaxial passage 36 therein and is provided with ports that furnishcommunication between the interior of the drum and said passage. Shaft35 communicates with a stationary effluent outlet pipe 38 which extendsto a point within the drum through a suitable packing gland or rotatingseal 39 positioned-within drum 34.

Stationary effluent outlet pipe 38 has extending through the sectionthereof that passes through the wall of tank 32 an air pipe 45 which isdesigned for free air flow without control means and extends from apoint outside the tank 32 to a point a short distance within the endwall of the drum 34 and adjacent the seal 39. Air pipe 45 has an airoutlet section 450 which extends through the sidewall of outlet pipe 38so that the open end thereof communicates with the atmosphere and isfree draining outside the tank 32 and a section 45b which extendsupwardly through the wall of the section of liquid outlet pipe 38 whichis within said drum to a point within the segment of drum 34 where airaccumulates.

As the drum 34 rotates, the surface of the bottom peripheral segment ofthe drum is contacted by air streams flowing from jets 40, 41 and 42which communicate with an air header 43 which also serves to support gasdispersers 44 that provide the agitation required to keep the solidscontent of the liquid in suspension. As the half of the peripheralsurface of drum 34, moving through the semi-circular path, above thehorizontal diametrical axis approaches the point 14 are where movementwill be below the horizontal diametrical axis, any solids which may beadhering thereto are dislodged preferably by an ultrasonic transducer 46mounted in a fixed position within said drum 34.

In the embodiment illustrated in FIG. 3, the numeral 32 indicates thetank into which a solids suspension is introduced by suitable means.

Liquid in the suspension passes through the porous peripheral surface 47of a rotatable drum 48. Rotatable drum 48 is supported by a centralshaft 49 which shaft is in turn supported by a bearing 49a secured inthe wall of tank 32 so as to be completely submerged in the suspension.Drum 48 rotates about central shaft 49 which has a central axial passage50 therethrough and is provided with ports 51 that furnish communicationbetween said passage and the liquid holding interior of said drum. Shaft49 communicates with a stationary liquid outlet pipe 52 through asuitable packing gland of rotatable seal 53. Outlet pipe 52 extends fromoutside the tank to a point within the drum 48 through a combinationbearing-seal means 54 which also provide support for the liquid outletend of said drum.

As the drum 48 rotates, irrespective of direction, the surface of thebottom peripheral segment thereof is contacted by streams of risingbubbles flowing from a plurality of gas dispersers 55 such as the typeformed by wrapping cord about a hollow foraminated core or by attachinga cloth sleeve member to a fixture having an air passage therethroughadapted to communicate with the interior of the sleeve. Dispersers 55are supported by their connection with a header 56.

Agitation to maintain the solids in the suspension is provided byinjection of air through dispersers 57 positioned adjacent the bottom ofthe tank which dispersers communicate with an air header 58. As the drum48 rotates and approaches the area where the surface of the drum issubject to the impinging action of rising gas bubbles, any solids whichmay adhere thereto are dislodged preferably by an ultrasonic transducer59 illustrated as mounted in a fixed position within said drum 48. Thisis the preferable position, but said transducer may be positionedoutside said drum.

Liquid outlet pipe 52 has within it an air pipe 60 which is designed forfree air flow and extends through that position of said means fordischarging clarified liquid which extends through said bearing-sealmeans 54 from a point outside the tank 32 to a point within the drum 48adjacent the seal 53. Air pipe 60 has an air outlet section or branch60a, which extends through the wall of liquid outlet pipe 52 so that theopen end thereof communicates with the atmosphere outside tank 32 and asection or branch 60b which extends upwardly through the wall of thesection of stationary outlet pipe 52 and through the space initiallybounded by said seal 53 and the end wall of drum 48, to a point withinthe segment of drum 48 where air accumulates.

In the embodiment illustrated in FIG. 4, the numeral 62 indicates a tankinto which a solids suspension is introduced by suitable means.

Liquid of the suspension passes through the porous peripheral surface 63of a rotatable drum 64. Rotatable drum 64 is completely submerged in thesuspension. Drum 64 rotates about a central shaft 65 which has a centralaxial passage 66 therein and is provided with ports that furnishcommunication between said passage and the interior of said drum. Shaft65 communicates with outlet pipe 67 through a suitable packing gland orrotatable seal.

As the drum 64 rotates, the surface of the bottom peripheral segmentthereof is contacted by liquid streams flowing from jets 68, 69 and 70.Liquid discharged from the jets is liquid withdrawn from the tank 62through pipe 71 which communicates with a pump 72. Pump 72 dischargesliquid through conduit 73 which delivers the liquid to said jets.

Agitation to keep the solids in suspension in tank 62 is provided by gasintroduced by means of dispersers 74. Dispersers are supported by theircommunication connections with a header 75 which delivers air from asource that is not shown.

Liquid outlet pipe 66 has within it an air pipe 76 which extends from apoint outside tank 62 to a point within the drum 64. Air pipe 76 has anair outlet section 76a which extends through the wall of liquid outletpipe 66 so that the open end thereof communicates with the atmosphereoutside tank 62 and a section 76b which extends upwardly through thewall of pipe 66 through the space inside of said drum and adjacent theend wall of drum 64 to a point within the segment of drum 64 where airaccumulates.

We claim:

1. Apparatus for clarifying a liquid suspension comprising a containerfor said suspension, means for introducing said liquid suspension intosaid container, a movable porous drum provided with a peripheral surfacescreen which separates the introduced liquid suspension from a zone forclarified liquid, means submerged in said suspension and positionedbelow the bottom segment of said movable porous drum for directing fluidinto impingement contact with said drum to dislodge solids which arebrought into contact with said movable drum by the liquid that passestherethrough, piping means for discharging liquid from said zone forclarified liquid extending from outside said tank to within said drumthrough a bearing-seal means and an air conduit extending thru thatportion of said piping means for discharging clarified liquid whichpasses thru said bearing-seal means with a branch within said drum whichextends through the wall of said piping means for discharging liquidupwardly to the segment within said drum where air accumulates and abranch outside said tank which extends thru the wall of said pipingmeans for discharging liquid for communication with the atmosphere.

